fix: allow dictionary values to be empty

[slarse]

Partial fix for #2 addressing only the value part of it.

I've encountered a lot of empty values in dictionaries in the wild, which currently breaks parsing. The fix here is to simply make dictionary values "zero or more", as specified in Bruno's grammar.

Making dictionary keys (and assert keys) zero or more is much more problematic, it leads to tons of parsing errors. I found through trial and error that marking them as optional instead appears to work fine, but then you end up with dictionary pairs that lack keys in the syntax tree which also isn't quite right.

Anyway, just having the value be zero or more characters solves my current issue, I just have a lot of empty values in files I'm working with.

[Scalamando]

Thanks for the PR!

Bruno's grammar is a little weird in that regard. I've also tried to get empty keys to work without removing the key token, but no luck yet.

Nevertheless, your contribution is already very valuable. Having empty values likely is a common scenario, as you pointed out.